1. Field of the Invention
The present invention relates to a laser processing device configured to carry out laser processing while controlling a gap between a processing nozzle and an object to be processed, and relates to a controller of the laser processing device.
2. Description of the Related Art
Generally, in laser processing using a laser processing machine, gap control is carried out, in which a processing nozzle approaches an object to be processed and a distance (gap) between the object and the processing nozzle is maintained. In this case, feedback control, in which an output from a position detector for detecting the position of the processing nozzle is used, is switched to the gap control in which an output from a gap sensor for detecting the distance between the processing nozzle and the object is used.
As a relevant prior art document, JP H09-308979 A discloses a laser processing device for reducing a movement time of a copy approach motion, by: generating a movement command during the copy approach motion based on copy approach velocity information, acceleration information, deceleration stopping distance information and distance information up to a gap reference position; and accelerating/decelerating the copy approach motion from a retreat position to a reference position of the copy motion, based on predetermined velocity information and acceleration information, while using information from a gap sensor as the distance information.
Further, JP 2010-125518 A discloses a laser processing device including: a control axis to which a processing nozzle is attached; a driving part for driving the control axis so that the processing nozzle is moved toward or away from an object to be processed; a servo controlling part for controlling the driving part; a position detecting part for detecting the position of the driving part; and a gap sensor for detecting a gap between the processing nozzle and the object. In this document, it is described that the servo controlling part changes the position of the driving part detected by the position detecting part based on a gap detection value detected by the gap sensor, and gap control is carried out so as to maintain the gap between the processing nozzle and the object.
FIG. 6 shows a temporal change in a velocity command value for approach motion in a conventional laser processing machine. First, (a control axis for driving) a processing nozzle is operated based on a first velocity command value 102. In detail, the processing nozzle is accelerated to maximum approach velocity Fa (region 104), and the processing nozzle is moved at constant velocity Fa until an output from a gap sensor corresponds to a deceleration start distance region 106. After that, the processing nozzle is decelerated at a predetermined deceleration rate (region 108). In this regard, “Td” in FIG. 6 represents a time point when the output of the gap sensor is equal to the deceleration start distance.
During the deceleration motion (region 108), first velocity command value 102 is switched to a second velocity command value 110 generated based on the output of the gap sensor. Concretely, at a point 112 (or time point x) where first velocity command value 102 is equal to second velocity command value 110, the velocity command value for controlling the motion of the processing nozzle is switched from first velocity command value 102 to second velocity command value 110.
However, in this case, since the velocity of the processing nozzle is rapidly changed at time point x, the processing nozzle is shocked at the time when switching the velocity command value, whereby the gap control thereafter may be adversely affected. Therefore, when the approach motion is adjusted, it is necessary to determine a parameter (or the deceleration start position) so as to smoothly switch the velocity command value. On the other hand, it is preferable that the approach time (or time Tf when the second velocity command value is equal to zero) be short as possible, whereas such adjustment is difficult and cumbersome.